1. Field of the Invention
The present invention relates to an orthogonal type three-axis robot used for mounting or removing parts into or from a printed board or the like and, and a control method for effecting a height control.
2. Description of Related Art
Orthogonal type three-axis robots are conventionally used for industrial purposes, and have a function to package parts into or remove parts from a printed board. The orthogonal type three-axis robot used in an MDF (Main Distributing Frame) is operative to insert or remove a connection pin into or from a hole formed in a matrix board 1 which is a form of printed boards. FIG. 1 is a plan view showing a matrix board 1, while FIGS. 2 and 3 show perspective views of a through hole 2 and a connection pin 3, respectively. FIG. 4 is a perspective view generally showing an example of the conventional orthogonal type three-axis robot.
As shown in FIG. 1, formed on the matrix board 1 are a plurality of lines Lx.sub.l, to Lx.sub.N (N is a natural number) on a primary side (referred to as primary lines hereinafter), and a plurality of lines Ly.sub.l to Ly.sub.M on a secondary side (referred to as secondary lines hereinafter). When an arbitrary one Lx.sub.n of the primary lines Lx.sub.l to Lx.sub.N and an arbitrary one Ly.sub.m of the secondary lines Ly.sub.l to Ly.sub.M of the secondary lines Ly.sub.l to Ly.sub.M are to be connected to each other, it is only necessary to connect the line Lx.sub.n to line Ly.sub.m at a point where the lines cross each other. For the purpose, the through holes 2 are proved at points where each of the primary lines Lx.sub.l to Lx.sub.N crosses each of the secondary lines Ly.sub.l to Ly.sub.M. When the connection pin 3 is inserted into the through hole 2 at a point where the line Lx.sub.n crosses the line Ly.sub.m, the line Lx.sub.n and the line Ly.sub.m are connected to each other, thereby one communication line that creates linking between the primary and secondary sides is formed.
The matrix board 1 has a multi-layered structure as represented by its cross section shown in FIG. 2, in which the lines Lx.sub.l to Lx.sub.N are formed in one of the layers, while the lines Ly.sub.l to Ly.sub.M are formed in another layer. The connection pin 3, on the other hand, has a circular cylinder-shaped head section 3a, and a rod-shaped under-neck section 3b extending from the head section 3a, as illustrated in FIG. 3. The head section 3a and under-neck section 3b are made from such a material as an insulating plastic, and a gold plating 3c is applied over the circumferential surface of an intermediate section of the under-neck section 3b. With this structure, the gold plating 3c is used for the connection between the lines Lx.sub.l and Lx.sub.N and lines Ly.sub.l to Ly.sub.m, and the length of the gold plating 3c is made equal to a distance between the lines Lx.sub.l to Lx.sub.N and lines Ly.sub.l to Ly.sub.M in the height or thickness direction. By inserting the connection pin 3 into the through-hole 2 until the under-neck section 3b described above contacts the layers having the primary and secondary lines, a desired one of the lines Lx.sub.l to Lx.sub.N can selectively be connected to a desired one of the lines Ly.sub.l to Ly.sub.M .
FIG. 4 shows an orthogonal type three-axis robot used for inserting the connection pin 3 at a specified position on the matrix board 1 shown in FIG. 1, in which a frame 11 facing a mother board 10 on which a plurality of matrix boards 1 are carried is provided. The frame 11 comprises four supporting elements 11a, 11b, 11c, and 1d which together form a rectangular shape, and provided between the supporting elements 11b and 11d, which are opposite to each other, is a movable supporting element 12 which can freely move in the longitudinal direction of the supporting elements 11b, 11d, namely in the direction of X-axis, which is a lateral direction of the matrix board 1. An X-axis step motor is provided on the supporting element 11b, and X-axis belts 14a, 14b driven by the X-axis step motor and moving the supporting element 12 are attached to the supporting element 11b and supporting element 11d respectively.
Provided on the supporting element 12 are a hand element 15 made of a metal material, which is typically shown in FIG. 5, and functions as a holding device for holding the connection pin 3, a hand opening and closing direct current (DC) motor 16 for opening or closing the hand element 15, a Z-axis step motor 17 for moving a position of the hand element 15 in the height or thickness direction, namely in the direction of Z axis, a Y-axis step motor 18, and a Y-axis feed belt 19 driven by the Y-axis step motor 18 which moves the hand element 15, hand opening and closing DC motor 16, and Z-axis step motor 17 in the longitudinal direction of the matrix board 1, namely the direction of Y-axis.
To minimize an installation area of the orthogonal type three-axis robot, for instance, four matrix boards 1 are fixed to the mother board 10, and two mother boards 10 are provided on both sides of the robot. Provided on each mother board 10 are a plurality of connectors 10a for accommodating the primary lines Lx.sub.l to Lx.sub.N and secondary-lines Ly.sub.l to Ly.sub.N for each board. A step motor is used for each of the motors 13, 17, 18 in order to reduce the cost of the robot. A cylinder may also be used in place of the DC motor 16 for opening or closing the hand element 15.
Now, description is made for operations for mounting (or, inserting) the connection pin 3 by the orthogonal type three-axis robot shown in FIG. 4.
The robot first checks the position of an original point on each of the matrix boards 1 upon start of the power supply, and then moves the hand element 15 to an original point Po on a target matrix board 1 by driving the step motors 13, 17, and 18. Instructions regarding the position for inserting the connection pin 3 are given to the robot from a system of a higher rank. The inserting position is given as relative moving distances of the hand element 15 in the directions of X, Y, and Z-axes from the original position Po. After the hand element 15 returns to the original position Po, the robot computes the height of the board 1 for determining the height of a working surface of the hand element 15, by using the hand element 15 as a measuring device for measuring the height of the matrix board 1.
FIG. 5 is a side view showing a relation between the board and hand element in FIG. 4.
Provided on the surface of each board 1 and projecting therefrom is a reference point PI for the measurement of height. This reference point PI is, for instance, made from metal, and is connected to a ground layer provided on a rear surface of the board 1. The robot moves the hand element 15 to a position above (in the direction of Z axis) the reference point PI in the state where a voltage is loaded thereto. Then the robot moves the hand element 15 toward the matrix board 1 in the direction of Z axis until the hand element 15 comes into contact with the reference point PI. As a result of this contact, a current flows from the hand element 15 to the ground, and a height of the reference point PI is measured by using a moving distance of the hand element 15 in the direction of Z axis. The height of the reference point PI measured as described above is stored as the height of the matrix board 1.
After this step, the robot performs the position control of the hand element 15 in the direction of X axis, the direction of Y axis, and the direction of Z axis based on an inserting position of the connection pin 3 is given by the system of higher rank and the height of the board 1, and inserts the connection pin 3 into a specified position of the board 1.
However, when inserting the connection pin 3 by using a conventional method of controlling the height of an orthogonal type three-axis robot, the following problem has been encountered.
Namely, if there exists any distortion in the direction of height in a mother board 10 serving as a base for each matrix board 1 or in the matrix board 1 itself, sometimes the connection pin 3 cannot be inserted into the through-hole 2 at some of the inserting positions, or connection fault may be generated between the primary lines Lx.sub.l to Lx.sub.N and secondary lines Ly.sub.l to Ly.sub.m on the matrix board 1. For this reason, not only reduction in working ratio of the robot, but also degrading of the connection quality are often experienced.
To solve the problems as described above, the following scheme is adopted according a first aspect of the present invention. In a method for controlling an orthogonal type three-axis robot which comprises a holding device for holding a part to be mounted on a board fixed on a base, or for removing a part to be removed from the board, provided is a driving system for supporting the holding device relative to the base and at the same time moving the holding device in a direction of X-axis which is a lateral direction of the board, in a direction of Y-axis which is a longitudinal direction of the board, and in a direction of Z-axis which is a direction of height or thickness of the board. Also provided is a measuring device for measuring a height or Z-axis coordinate of a surface of the board. The driving system moves the holding device in the direction of X-axis as well as in the direction of Y-axis, and also moves the holding device in the direction of Z-axis according to the measured height or Z-axis coordinate for adjusting a height or Z-axis coordinate position of the holding device to a height or Z-axis coordinate of a board surface to which or from which a part is to be mounted or removed. At a plurality of specified positions, a step is provided for correcting a moving distance of the holding device in the direction of Z-axis, when moved by the driving device, for each of the specified positions.
According to a second aspect of the present invention, in the method for controlling an orthogonal type three-axis robot according to the first aspect of the present invention, at first, heights, i.e. the Z axis coordinates, of four points which form a rectangle on the surface of the board and measured by the measuring device. Then, by using X, Y, and Z (height) coordinates of three points among the four points, a height or Z-axis coordinate of each specified position located inside an area of the three points is estimated, and a moving distance in the direction of Z axis, when the holding device is moved by the driving system, is corrected according to the estimated height or Z-axis coordinate.
According to a third aspect of the present invention, in the method for controlling an orthogonal type three-axis robot according to the first aspect of the invention, at first, heights, i.e. the Z-axis coordinates of four points forming a rectangle on a surface of the board and a height or Z-axis coordinate of a point inside the rectangle are measured by the measuring device. Then, from X and Y coordinates and heights or Z-axis coordinates of two points from among the four points forming the rectangle, and a height or Z-axis coordinate of one point inside the rectangle, a height or Z-axis coordinate of each of the specified positions inside a triangle formed by these three points is estimated respectively, and a moving distance in the direction of Z axis, when the holding device is moved by the driving system, is corrected according to the estimated height or Z axis coordinate.
According to a fourth aspect of the present invention, there is provided an orthogonal three-axis robot comprising a holding device for holding a part to be mounted on a board fixed on a base, or for removing a part to be removed from the board; a driving system for supporting the holding device above or relative to the base and moving the holding device in a direction of X axis which is a lateral direction of the board, in a direction of Y axis which is a longitudinal direction thereof, and in a direction of Z axis which is a height or thickness direction thereof; and a measuring device for measuring a height or Z-axis coordinate of a surface of the board. The holding device is moved in the direction of X axis well as in the direction of Y axis by the driving system, and also is moved in the direction of Z axis according to the measured height or Z-axis coordinate to adjust a height or Z-axis coordinate of the holding device to a height or Z-axis coordinate of a surface of the board, and then mounts or removes a part on or from the board, wherein by the driving system, a moving distance thereof in the direction of Z axis, when moving the holding device, is corrected for each of the specified positions.
According to a fifth aspect of the present invention, in the orthogonal type three-type robot according to the fourth aspect of the present invention, the measuring device and the driving system are configured to perform the following operations.
Namely, the measuring device is operative to measure heights, i.e. Z axis coordinates, of the four points forming a rectangular form on a surface of the board, and the driving system is operative to estimate, from X coordinates and Y coordinates of three points of the four points, a height or Z-axis coordinate of each of the specified positions inside a triangle formed by the three points, respectively, and to correct, when moving the holding device with the driving system, a moving distance in the direction of Z axis according to the estimated height or Z-axis coordinate.
According to a sixth aspect of the present invention, in the orthogonal type three-axis robot according to the fourth aspect of the present invention, the measuring device and the driving system are configured to perform the following operations.
Namely, the measuring device is operative to measure heights, i.e. Z-axis coordinates, of four points forming a rectangular form on a surface of the board and a height, i.e. Z-axis coordinate, of one point inside the rectangular form, and the driving system is operative to estimate, from X coordinates and Y coordinates as well as the heights or Z coordinates of two points of the four points forming the rectangular form, and also from an X coordinate and a Y coordinate as well as a height or Z coordinate of the specified position inside the rectangle, a height or Z coordinate of the specified position inside a triangle formed by these three points for each specified position, respectively, and to correct a moving distance in the direction of Z axis, when moving the holding device with the driving system, according to the estimated height or Z coordinate for each of the specified positions, respectively.
According to the features relating to the first to sixth aspects of the present invention, the method includes controlling the orthogonal type three-axis robot having the configuration as described above, in which the holding device is moved by the driving system to a specified position on the board, and the orthogonal type three-axis robot mounts a part on the board at a specified position or removes a part which has been mounted on the board. Furthermore, with the configuration described above, even if there exists any distortion in a height or thickness direction of the board due to inclination of the base or for some other reason, the height or Z coordinate of the holding device can be corrected for each position at which parts are mounted to or removed from the board. For this reason, the problems encountered in the prior art described before are completely eliminated.